Abstract 11707: Increased Binding Between Titin and Murf1 is Associated with Hypertrophic Cardiomyopathy in a Fish Model and in Human Patients
Background: Hypertrophic cardiomyopathy (HCM) is a hereditary disease characterized by cardiac hypertrophy with diastolic dysfunction. Gene mutations causing HCM have been found in about half of HCM patients, but there are many patients with unknown genetic etiology and their pathogenesis has not been fully clarified
Methods and Results: To decipher a novel mechanism for the pathogenesis, we performed N-ethyl-N-nitrosourea (ENU) mutagenesis screening and identified a non spring heart (nsh) fish mutant, which showed diastolic dysfunction and hypertrophic heart. The nsh mutant heart lost elasticity and beat in a rigid manner. Immunohistochemistry and transmission electron microscopy of the nsh homozygous mutants revealed significantly fewer myofibrils and disrupted sarcomeric structures. Titin isoform shifts showed a decreased elasticity pattern in the nsh heart. In addition, the myofibrils of the nsh heterozygous mutants showed M-line disassembly, similar to the pathological changes found in HCM patients. Positional cloning of nsh mutant revealed a missense mutation in an immunoglobulin (Ig) domain located in the M-line-A-band transition zone of titin, leading to Asp23186Val around the binding site for muscle-specific ring finger protein 1 (MURF1). MURF1 is a sarcomere-associated E3 ubiquitin ligase that regulates protein turnover. The nsh mutants showed reduced expression of A-I junction containing the Titin isoform and faster degradation, although the expressions of α-actinin, myosin, and C-terminal containing the Titin isoform were unchanged. Analysis of 96 genetically unrelated Japanese patients with familial HCM identified two disease-associated mutations in the other Ig domains of the M-line-A-band transition zone of titin. Co-immunoprecipitation assays of the binding between MURF1 and titin Ig domains with or without the mutations revealed that the mutations found in fish, and familial HCM, increased binding of titin to MURF1. This suggests the pathogenesis underlying the titin-M-line-A-band transition zone-related HCM might be a consequence of enhanced protein turnover.
Conclusion: The impaired interaction between titin and MURF1 is a novel mechanism for the pathogenesis of HCM.
- © 2011 by American Heart Association, Inc.